native pyproject.toml config

[gaborbernat]

This is a ticket to track and implement a native pyproject.toml configuration. Will update with the proposed plan and format.

Core goals:

• explicitly inheritance based (a lot of substitution at the moment is used to replicate inheritance),
• substitution able,
• reasonably familiar (e.g. share most concepts with ini format),
• succinct (some form of factors needs to have).

We'll use this opportunity to rename some keys (e.g. skipsdist should be skip_packaging, etc).

[obestwalter]

Learning from the old format, I would add:

• easy to debug (good visualization of the settings - `--showconfig`` 2.0)
• conservative error handling (err on the side of crashing early with a helpful error, rather than being too allowing for "creative" uses)

[obestwalter]

... and most importantly: a clear, versioned specification that can then evolve as we for sure won't get it right at first try :)

[obestwalter]

I think, It would be great if we could organize a sprint around this whole topic at some point this year.

[gaborbernat]

Well, most importantly we need someone try to tackle this and implement it. Personally, in my priority queue, this is quite low. I've tackled it inside https://github.com/gaborbernat/toxn/blob/master/pyproject.toml#L5 only to prove it's quite hard to get this right. I'll only have some bandwidth for this after the #1102, #998 and #338. I also want to first split up configuration module from a mega file to sub-modules.

GitHub

gaborbernat/toxn

toxn aims to automate and standardize testing in Python - next generation tox - gaborbernat/toxn

[obestwalter]

That's exactly why I think a sprint with a few more people might be a good way to get this off the ground. Maybe around a conference where a few of as will go anyway - e.g. EuroPython.

[gaborbernat]

I don't consider this a good candidate for a sprint. That creates an artificial deadline (e.g. end of sprint). Instead, we should probably propose each and every one of us our own proposal and iterate on that until we find something that can do at least what the ini does at the moment. With toxn I had to start over a few times just because halfway through I figured well this path makes feature x/y really hard to support/implement.

[ionelmc]

Why not a tox.toml? pyproject.toml is going to be a mess (just like setup.cfg was when people decided to make tools that rewrite/change stuff in it).

[obestwalter]

@gaborbernat

That creates an artificial deadline (e.g. end of sprint).

Only in your head :) A sprint would in my eyes be a good way to make progress and share state, but in no way a deadline. Especially if you explored that area already with your toxn fork, you could share what you learned and we could take it from there.

@ionelmc

Why not a tox.toml?

That would be simply the [tool.tox] part of pyproject.toml, so that comes pretty much free with it. As a user I would definitely also want the possibility to configure tox still in an extra file if it is more involved.

pyproject.toml is going to be a mess (just like setup.cfg was when people decided to make tools that rewrite/change stuff in it).

Why do you think that? I might be a bit naive because I am really not that deep in the whole packaging topic, but I am pretty hopeful that this time around we'll do things better.

[gaborbernat]

I don't think it's going to be a mess. But it definitely can be hard to maintain once many things will try to use it. E.g. a complex tox + towncrier + black config can easily make pyproject.toml 200+ lines. I think there's no reason to limit ourselves to pyproject.toml only. I would say let's have by default tox section inside pyproject.toml, but fallback to tox.toml who want to separate it out.

[ionelmc]

Why do you think that? I might be a bit naive because I am really not that deep in the whole packaging topic, but I am pretty hopeful that this time around we'll do things better.

Well ... how to put it ... I've looked at https://github.com/gaborbernat/toxn/blob/master/pyproject.toml#L5 and I thought "well I don't want to write all those ridiculously long section names, I'd already be at my wits' end after all those quotes and brackets".

The second thing is that there will inevitably be broken tools that try to modify pyproject.toml - eg: bumpversion rewrites setup.cfg (if you're naive enough to use that - I was) but with slightly different values for the other sections.

From my perspective the only benefit of toml is that tox will get more features.

To give a bit more perspective, pyproject.toml is the new hotness but also these were too the new hotness some years ago:

• setuptools - turned out to be a huge pile of buggy monkeypatching
• distribute - turned out to be a huge pile of evil monkeypatching, but with different bugs - remember those projects that messed up your python installation cause they bundled a distribute_setup.py that tried to replace installed setuptools with distribute? i do
• disutils2 - an abandoned reimplementation of distutils

What I'm getting at here: ignore the PEP518/pyproject.toml bandwagon - just think about a new configuration system for tox.

GitHub

gaborbernat/toxn

toxn aims to automate and standardize testing in Python - next generation tox - gaborbernat/toxn

[gaborbernat]

I'm a bit conflicted here now though, I don't think we can come up with anything as succinct as our current ini format. So if writing brackets and quotes is going to become a problem (which very easily could be, I found myself to be a bit awkward when I've created toxn), I don't think there's much benefit from moving off the ini format.

[ionelmc]

Hmmm, can you elaborate a bit more on this goal:

explicitly inheritance based (a lot of substitution at the moment is used to replicate inheritance)

[joernheissler]

Why TOML?

There are some arguments here, most of which I support: https://gist.github.com/njsmith/78f68204c5d969f8c8bc645ef77d4a8f
What's missing are the security issues of YAML (never use yaml.load!). Aside from that, I don't have any problems using yaml, it works great for me.

I don't like TOML either (horrible syntax for nested data structures) and would have wished for some simplified YAML instead, but looks like pyproject.toml is the new standard.

JSON and YAML do have schema verification

Can't you decode the TOML and then verify the schema? I think that YAML supports everything that can be expressed in TOML (and more) so a YAML validator could be adapted to TOML easily.

[gaborbernat]

This will be possible with #1394, ETA at least September.

[ssbarnea]

@gaborbernat Maybe you can get some inspiration from https://gohugo.io/getting-started/configuration/#configuration-file which had a more flexible approach, avoiding making a decision for the config file format. In the end a config file is expected to be a nested dictionary, bit of flexibility avoided endless debates.

Regarding the conditionals question I forgot to answer. At this moment tox already does this in a various ways, for practical reasons:

• {tty:foo:bar} is a conditional
• the envname: prefix on dependencies is another hidden way to implement conditionals, so you can add a dependency only to specific environment.
• {env:FOO:default} is another kind of implementing simple conditionals based on environment values.

We should step back a little and try to see how projects are stretching the tox use and seeing how often people end-up writing bash scripts that run more complex code after realizing they waste too much time writing escapes with some bash -c "..." constructs. I am not referring to specific project, I am referring to tox.ini in general and especially across bigger projects. I am mentioning this because that refactoring would be the time to consider addressing these limitations.

For example, one thing that I like about YAML was that it was extremely simple to add a multiline string as a value, so I could easily avoid adding an extra file with a 5-10 line shell script and just embed it (indentation is the only thing needed).

A reminder to other users: you still need to control your language and follow https://github.com/tox-dev/tox/blob/master/CODE_OF_CONDUCT.md -- While I would find acceptable to hear some comments over a beer debate, try to stick to facts and avoiding attacking other entities.

[stefansjs]

so... I'm not sure about the original intention behind this ticket, but to me the most obvious reason to allow pyproject.toml has nothing to do with the superiority of toml over ini (debatable, but not the point), but the centralization of project configuration in one file. As a user, I would be very happy to avoid another configuration file if it meant I could fully specify build and test environments in one place. I believe this is the spirit of allowing extra sections in pyproject.toml in the PEP

Is there a reason in particular we can't just transliterate the current ini features into toml?

[gaborbernat]

Because the ini offers a lot of flexibility/functionality that's not easy to express within TOML, e.g. conditional factors and value substituion.

[ssbarnea]

tox usage of ini is the most complex use of the ini "format" I ever have seen. It is quite a complex DSL, even so for basic usage you do not need to read the docs. I am not saying that I love or hate it but porting it to TOML would likely end up as a disaster due to incompatible/conflicting syntax.

My impression is that tox should fix other areas before changing the configuration file format. IMHO, if the tox config should have to be rewritten, it would as well be an opportunity for the user to switch to another tool.

It may worth noting that the all tool configuration in a single file may be the wrong solution for the issue of cluttering the project root folder, especially if the tools involved are likely to have bigger configuration files with more changes to them like tox. For linters I do not see a real problem to stick them to pyproject but if you try to stick everything in, you end up with a maintenance issue, problematic backporting to stable branches and merge conflicts on bigger projects.

As I was also annoyed by the cluttering of the project root folder I started to allow configuration loading from .config folder, which is based on XDG_CONFIG_HOME -- there are several tools that can keep their config files in a subfolder. While the XDG standard refers to user home, there is nothing wrong in applying the same concepts relative to the repository root.

[gaborbernat]

I can see the appeal in having a TOML config. And we'll likely have one in tox 4. tox 4 (see rewrite branch) does a clean separation via abstraction on where the source comes from and how it is translated to python configuration objects - see https://github.com/tox-dev/tox/blob/rewrite/src/tox/config/source/__init__.py#L10. With that, we can implement a toml configuration format for tox that maybe is less succinct than the ini one, however, for simple cases is good enough. Such separation of abstractions is not present in tox 3, and introducing those is hard without breaking a lot of our plugins. Hence, why we haven't done this yet.

With that being said tox 4 is likely not to happen before the end of the year but hopeful for an RC in January. So in the meantime, this is blocked.

[ChihweiLHBird]

Is the work related to this issue still in schedule?

[jugmac00]

The current focus is on getting tox 4 ready for a final release. Just last week the final alpha was released.

This feature was scheduled for 4.1. Once we get tox 4 out, there will be quite a transition period and possibly quite some edge cases coming up which need attention.

That said - let's see what @gaborbernat has to add.

[gaborbernat]

Mostly what @jugmac00 said. The design of the tox 4 is made to allow this without too much of heavy-lift but I'd not pull myself into this when trying to make tox 4 actually come out the door. But would like to follow up on this quickly after that happens.

[ChihweiLHBird]

Thank you for the information! @jugmac00 @gaborbernat

[bagel897]

1. Could tox use the pyproject.toml to detect the supported python versions and use those?
2. If it helps, I'm making a library to support toml and ini configuration

[gaborbernat]

Thanks, but that will not help. tox configuration is complex and it's not possible to have the same config in ini and toml. E.g. substitutions and references don't work well in toml, so we need to design a config file/logic that's better suited for TOML.

[ketozhang]

@gaborbernat Since this issue has gotten as complicated as it is, it would be useful to have a writeup of the complexities you've mentioned.

[gaborbernat]

Mostly boils down to the ini logic cannot be used by the pyproject.toml file. That's because a TOML file is a type bound structure, while ini is just raw strings.